1. Field of the Invention
The present invention relates to an electronic-circuit-component mounting system arranged to mount a plurality of electronic circuit components on a printed-wiring board, a method practiced in this system to obtain positioning errors of the printed-wiring board, a method of mounting the electronic circuit components, and programs for practicing those methods.
2. Discussion of Related Art
There is known an electronic-circuit-component mounting system which includes a plurality of component mounting units arranged along a straight line. Each of the component mounting units is provided with a mounting head and a head moving device operable to move the mounting head. This electronic-circuit-component mounting system is arranged such that at least two of the component mounting units are concurrently operated to mount electronic circuit components on one printed-wiring board. In the electronic-circuit-component mounting system of this type, each printed-wiring board is positioned such that areas of movements of the mounting heads of the at least two component mounting unit cover respective parts of the printed-wiring board on which operations to mount the electronic circuit components are to be concurrently performed by the component mounting heads of the respective component mounting units.
In an electronic-circuit-component mounting system, each printed-wiring board is generally provided with a fiducial portion used to reduce positioning errors of electronic circuit components as mounted on the board, which would be caused by errors of positioning of the board relative to the component mounting units. In this case, a recognition device such as an imaging device is provided for each of the component mounting units, so that the positioning errors of each printed-wiring board relative to each component mounting unit is obtained on the basis of a result of recognition of the fiducial portion by the recognition device. When each electronic circuit component is mounted on the printed-wiring board, data representative of a predetermined position of the corresponding mounting head at which the electronic circuit component is to be mounted on the board are compensated to reduce at least the positioning errors of the board (horizontal positioning errors and an angular or rotational positioning error), and the operation to mount the electronic circuit component on the board is performed by the mounting head located at the compensated position. At this time of compensation, the position of the mounting head is usually compensated to reduce other positioning errors, such as errors of positioning (horizontal positioning errors and an angular positioning error) of the electronic circuit component as held by the mounting head. This compensation, which does not directly relate to the present invention, will not be further discussed herein.
Where the plurality of component mounting units are concurrently operated to perform operations to mount the electronic circuit components on one printed-wiring board, as described above, the board is provided with a plurality of fiducial portions in respective areas thereof corresponding to the respective component mounting units. These fiducial portions are recognized by respective recognition devices provided for the respective component mounting units, and the positioning errors of the printed-wiring board relative to the component mounting units are detected on the basis of outputs of the recognition devices, so that the electronic circuit components are mounted at predetermined positions by moving the mounting heads to the respective positions as compensated according to the detected positioning errors of the board. If the printed-wiring board has only one fiducial portion for each of the component mounting units, it is impossible to obtain the positioning errors of the board relative to each component mounting unit.
In view of the above drawback, there have been proposed the use of a mechanical positioning device and the use of a board-holding device and an imaging device. For example, the mechanical positioning device is arranged to insert positioning pins in a plurality of positioning holes formed in the printed-wiring board, for improving the accuracy of positioning of the printed-wiring board. The board-holding device, which takes the form of a pallet, for example, is arranged to hold the printed-wiring board at a fixed position, and the imaging device is arranged to detect errors of positioning of the board as held by the board-holding device, so that the board-holding device is repositioned with high accuracy on the basis of an output of the imaging device, to improve the positioning accuracy of the electronic circuit components as mounted on the board.
However, the mechanical positioning device is limited in the accuracy of positioning of the printed-wiring boards, and does not easily permit a sufficient improvement in the mounting accuracy of the electronic circuit components. On the other hand, the board-holding device which is arranged to fixedly hold the printed-wiring board thereon and which is repositioned with high accuracy suffers from a problem of an inevitable increase in its structural complexity and an accordingly increased cost of its manufacture.